Study On Analysis And Optimization Of The Combined Supporting Structure On The Frozen Construction Section Of Outlet Tunnel

In this paper, a domestic tunnel project was used as an example, for the existingjoint supporting measures on the frozen segment of a tunnel, the surrounding rock’sstability and force law on supporting structure are analyzed when the tunnel wasconstructed and after the soil was thawed. Evaluation has been done on the supportingmeasures,and proposed strengthen or optimization suggestions under the conditions inthe long run.In this paper, three-dimensional finite element method was used to simulatevarious reinforcement methods (lined with concrete, steel mesh, steel support, hoopreinforcement, longitudinal reinforcement, etc.), the contact elements was used tosimulate the interaction of the segment between the tube and the tube sheet and tubeand pea gravel the cushion, the different calculation conditions was considered, thestructural analysis was conducted on the two suggested supporting methods,and aanalyzing comparison was done with the enhancement measures.（1）For the existing support program one, in the case of extreme checking loadsand the geological survey parameters of unconsolidated sandstone, the safetyrequirements of the project running can not be guaranteed, in order to ensure thesecurity of long-term operation under the supporting structure, there is a need totaking effective measures to improve the elasticity modulus of the unconsolidatedsandstone around the hole to100MPa by the measure of grouting effectively, andmake the spacing between the steel arch be dense to40cm meanwhile. With thedesign load of soil-water pressure which is measured as1.1MPa, the elasticitymodulus of the existing unconsolidated sandstone has obvious impact on the force ofsupport structure, taking the upper limit of60MPa, the requirement of stability andthe safety of support structure of the tunnel can be met; when lower limit is30MPa,the support structure doesn’t have safety margin and has great risk. Recommendedspacing between the steel arch is40cm, and take effective drainage measure duringthe construction, reducing the soil-water pressure around the hole.（2）For the existing program two, in the case of extreme checking loads and thegeological survey parameters of unconsolidated sandstone, the safety requirements ofthe project running can not be guaranteed, if the design load is1.1MPa as for themeasurement soil-water pressure and the elasticity modulus of unconsolidated sandstone is within limits of considering perturbation geological surveyparameters(20~60MPa), program tow can meet the requirements basicly. Through theanalysis of sensitivity ratio of the elasticity modulus of unconsolidated sandstone,there is a need to improve the elasticity modulus(up to100MPa which isrecommended) and other mechanics index, and the spacing between the steel arch isrecommended to40cm, take effective drainage measure during the construction,reducing the soil-water pressure around the hole at the same time.（3）Compare the existing two programs, in the condition of geological surveyparameters of unconsolidated sandstone which is30MPa as lower limit and themeasurement soil-water pressure is1.1MPa, program two can basicly meet theengineering requirements but program one can not, in extreme condition, both twoprogram need to be strengthened. Considering that program two need expandedexcavation of the tunnel which is a disadvantage for engineering investment andconstruction period, so design reinforcement supporting on the basis of the existingprogram one is recommended.